A variety of pellet and like granular product coolers and dyers are available where the most common system for cooling pellets is the conveyor type such as disclosed in U.S. Pat. No. 4,991,351. The product is conveyed a considerable distance while cooling air is directed upwardly through the conveyor to cool the pellet product thereon. Usually the conveyors extend lengthwise, hence, considerable floor space is occupied by the conveyor coolers.
Examples of vertically orientated coolers are found in U.S. Pat. Nos. 4,445,282, 4,683,665 and 4,869,162. The advantage in providing a vertical cooling system is that less flow space is occupied. The problem however is to develop a vertically orientated cooler which can provide similar production rates as the common conveyor system. The cooler of U.S. Pat. No. 4,445,282 has a product inlet at the top of the bin with a product discharge at the base. A reciprocating grate is provided approximately mid-station of the bin to temporarily retain product on the grid. Air is drawn upwardly through the product by way of mounting a fan at the top of the bin to exhaust air from the upper region of the bin. The grate is reciprocated to cause a controlled yet slow downward flow of pellet product through the grate and out through the discharge bin. The grating comprises off-set but overlapping vertically spaced apart baffles which require that the product flow in a zig zag pattern in finding its way through the grate. Cooling air which flows upwardly through the grate tends to cause fluidization of the product above the grate. Although this can be beneficial from the standpoint of cooling the product and also removing surface moisture, such fluidization of the product can cause reduced flow rates of product through the material due to air resistance to a downward flow of product through the grating.
The vertical cooling system of U.S. Pat. No. 4,869,162 is similar in design to that of U.S. Pat. No. 4,445,282. However, the grating system on which the product is retained is of a slightly different design. Flat beams beneath angular shaped baffles reciprocate to cause the product to either be retained on the grate or when the beams are moved such that the spaces therebetween are aligned with spaces between the deflector plates, product flows freely downwardly into the discharge of the bin. When the spacing between the beams is aligned with the interior of the deflector plates air is directed through one or more channels and into the product to effect the cooling and drying thereof. The air flows upwardly through the spaces between the beams. However, as the beams are moved transversely of the deflector plates the air is cut off from the space beneath the deflector plates and is instead directed upwardly through the space between the beams and through the space between the deflector plates. This increased flow of air through this space causes fluidization of the pellet product therein. Either the flow rate of air is reduced to avoid fluidization of the product and hence, prolong the cooling and drying action or if higher air flow rates are retained, fluidization of the product results in reduced flow rates of pellet product through the grates.
A similar problem exists with respect to the vertical cooling tower of U.S. Pat. No. 4,683,665. In this system, an intermediate grate reciprocates relative to the lowermost grate. An uppermost grate remains stationary and has longitudinally extending vertical plates which retard lateral movement of the product as the intermediate and lowermost plates reciprocate. However, fluidization of the product occurs because when the intermediate and lowermost grates are in their one extreme position to provide maximum opening for product to flow downwardly, all air introduced to the system flows correspondingly upwardly through the same pathway. As already explained, for higher flow rates, this results in fluidization of the product and hence, retarding the downward flow of the product through the grating system. Conversely, to avoid product fluidization, the flow rates of air have to be reduced which prolongs the time in cooling the product to the desired temperature before further treating.
The apparatus according to this invention overcomes the above problems by providing a grate system having air deflector designs which provide enhanced cooling while minimizing fluidization of the product.